Tapered locking nut

ABSTRACT

A locking nut is provided by forming a straight cylindrical bore through a body, forming a tap with uniform teeth, the tips of which taper at a shallow angle toward one end of the tap, and tapping said bore with said tap so as to produce a thread having a pitch diameter and a root diameter which taper from one of the thread to the other, and a crest which is of constant diameter and increasingly truncated from one end to the other, said thread at said one end having substantially a full profile.

This is a division of application Ser. No. 362,032, filed Jun. 1, 1989,now U.S. Pat. No. 5,014,411.

BACKGROUND OF THE INVENTION

A chronic problem for threaded fasteners is the tendency of theconnection to loosen under vibration. One approach to a locking fastenerfor the aerospace industry has been to provide slots at one end of a nutand crimp the nut inwardly at that location so as to form aninterference when a bolt enters. The bolt then deflects the slotted partof the nut outwardly as it enters, and these sections of the nut act asresiliently deflected beams which bear inwardly against the surface ofthe bolt to create a locking effect. Another type of locking nut has anend portion that is uninterrupted but has a relatively thin wall whichis deflected to an out-of-round configuration. Entrance of the bolt intothe nut then tends to deflect the thin walled part back toward acircular shape so that this portion of the nut exerts a resilient forceagainst the bolt to prevent loosening under vibration.

Locking fasteners of these types have certain disadvantages. One is thatthe amount of inward deflection of the end of the nut cannot becontrolled with precision. When an end part of the nut is crimpedinwardly, some spring back will occur so that the exact configuration ofthe nut end cannot be established. In addition, nuts of this type can bereused only a limited number of times, because when deflected toward acylindrical shape a number of times they tend to assume a cylindricalshape and lose their ability to lock against the thread of the bolt.Furthermore, nuts of this type may cause galling of the threads when thebolt and nut are mated.

Consequently, there has existed a need for an effective and trouble freelocking nut.

SUMMARY OF THE INVENTION

The present invention provides an improved locking nut overcoming thedifficulties of the prior art. The nut of this invention does not relyupon a resilient beam effect and does not require crimping of the end ofthe nut. Instead, it provides for a controlled interference between thethread of the bolt and the nut, giving uniform results, repeatabilityand avoiding damage to the threads.

The blank used in forming the nut of this invention has no slotted orthin walled portion, hence being essentially undeflectable throughoutits length. A straight, cylindrical bore is formed through the nut. Thethread in the nut is cut by a special tap, which has teeth of the fullthread dimension set on a shallow taper, typically, an included angle of1° to 2°. This is much less taper than that of conventional pipethreads, for example. The tap is extended through the bore apredetermined distance, and then backed out rather than extended furtheras in conventional tapping. The thread cut in the nut has a pitchdiameter and a root diameter on the same taper as the tap, that is, atan included angle of around 1° to 2°. The crest of the thread, however,is a constant diameter from one end to the other. Because the tap istapered, it creates the root of the thread with a full dimension, butthe crest becomes increasingly truncated from one end to the other. Atthe entrance, however, both the crest and the root of the thread are ofsubstantially full dimension.

When the bolt then enters the nut it can thread inwardly withoutdifficulty at he entrance because of the full thread at that location.However, the bolt thread soon begins to interfere with the thread in thenut as the bolt progresses through the nut. The interference may becontrolled so that the torque required to mate the nut with the boltfalls within a specified range.

The interference between the thread of the bolt and the nut creates onlyhoop stress in the nut, and no beam type deflection. The locking effectis predictable and will in all instances prevent the loosening of theconnection due to vibration. Inasmuch as the nut has no conventionaldeflected elements, the amount of interference is known within a narrowrange of tolerances. The threaded connection can be mated and unmatedmany times without loss of effectiveness. The threads will not becomegalled as the nut is used. Moreover, the nut of this invention can beproduced with fewer operations and thus at a lower cost than that forproduction of conventional locknuts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a locking nut;

FIG. 2 is a longitudinal sectional view of the blank for forming the nutand the tap to produce the thread;

FIG. 3 is a view similar to FIG. 2, but with the tap inserted into thenut blank;

FIG. 4 is a fragmentary longitudinal sectional view of the nut matedwith a bolt; and

FIG. 5 is a greatly enlarged fragmentary sectional view of the thread ofthe locking nut.

DETAILED DESCRIPTION OF THE INVENTION

In producing the locking nut 10 there is first formed a nut blank 11shown in FIG. 2. The latter element includes a flat base 12 ofrelatively large diameter upon which it is adapted to be seated. Thebase 12 connects through an inclined exterior surface 13 to an exteriorsection 14 which is straight longitudinally and provided with wrenchingsurfaces of conventional configuration. The nut blank 12 is ofcontinuous wall and generally rigid and undeflectable throughout itslength. Interiorly, the bore of the nut blank 11 includes an enlargedentrance portion 15 extending inwardly from the base 12 and forming acounterbore. Beyond the entrance portion 15 to the beveled outer end 16,the bore 17 is defined by a right cylinder.

Threads are cut in the bore 17 by means of a tap 18, shown in FIG. 2,formed with cutting teeth 19, which are of the normal full dimension forproducing a standard thread. The cutting teeth 19 are positioned so asto be at a shallow taper toward the outer end 20 of the tap. This meansthat the tips of the teeth 19 converge toward the outer end 20,preferably at an included angle 21 of from 120 to 2°. For smaller sizes,the included angle 21 is closer to 1°, and the 2° taper is approachedfor larger sizes.

The tap 18 is rotated and advanced into the bore 17 of the nut blank 11from the entrance 15, which it clears. The advancement of the tap 18 iscontrolled so that it is moved axially relative to the nut blank 11 apredetermined distance, after which its rotation is reversed and it iswithdrawn. As a result, the thread 22 illustrated in FIG. 5, where it isgreatly enlarged, is produced. The pitch diameter 23 of this threadtapers at an included angle of 1° to 2°, or a half angle 24 of 0.5° to1.0°, from the entrance to the thread to its outer end 16. The diameterof the root 25 of the thread tapers similarly toward the outer end 16.Therefore, the flanks 26 of the thread move closer to the longitudinalaxis from the entrance 15 to the outer end 16. However, the crest 27 ofthe thread has a constant diameter.

The thread 22 produced in this manner has the full thread profile of astandard thread, or close to it, adjacent the entrance 15 to the thread.The crest 27, however, is truncated from this location to the outer end16. The truncation of the thread increases progressively toward theouter end 16. The taper thus produced should be such that a standard gogauge can enter the thread for at least 3/4 of a revolution. As thegreatly enlarged view, FIG. 5, depicts, the change in the thread fromone end to the other is slight because of the shallow taper of the tap.Nevertheless, it is sufficient to produce a locking effect.

The nut 10 then is complete and is ready to mate with a standard bolt 28which has a constant pitch diameter. The bolt 28 enters the thread 22freely because of the substantially full depth of the thread at itsentrance end. However, as the bolt approaches the outer end 16, aninterference is created between the bolt thread and the nut thread. Thisinterference, indicated by the phantom line in FIG. 5, effectivelyprevents loosening from vibration.

The interference can be established with precision so that the amount oftorque necessary to thread the bolt through the nut falls within apredetermined range. For example, for a 3/8-24 nut, the torque rangespecified in the aerospace industry is 91/2 to 40 inch-pounds. Althoughdifficult to achieve in the production of conventional locknuts, thereis no problem in meeting this torque requirement consistently with thelocknut of this invention. This result is obtained by the taper of thetap 18 and by control of the axial travel of the tap into the bore asthe thread 22 is formed.

This arrangement provides a controlled and accurate interference betweenthe bolt and the nut so that they may be made consistently to locktogether and resist loosening from vibration. Results are uniform andrepeatable through many cycles of mating the bolt and the nut, yetgalling of the threads is avoided.

In larger sizes, the nut may be provided with a short entrance portionof constant pitch diameter, beyond which is the tapered section of thethread.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims

What is claimed is:
 1. A locking nut comprising:a body having wrenchingsurfaces on its exterior, a base at one end upon which said body isadapted to be seated, and a threaded bore extending through said body,the thread of said bore having a pitch diameter which tapers toward theend opposite from said base, throughout the entire length of said bore,at and included angle of from about 1° to about 2°, having a fullyformed root having a taper similar to that of said pitch diameter, andhaving a crest which is of a constant diameter, said crest beingtruncated with the truncation increasing from adjacent said base toadjacent said opposite end, said thread being continuous anduninterrupted by axial grooves or beams, whereby when a bolt is threadedinto said nut the tread of said bolt will interface with said thread ofsaid nut to create a locking effect.
 2. The locking nut of claim 1,wherein said body is substantially rigid and substantially unbendable,such that said locking effect is created by interference between thethread of said bolt and the thread of said nut, without base deflection.3. In combination with an exteriorly threaded member of constantdiameter, a lock nut comprising:a body having a threaded bore extendingtherethrough, the thread of said bore being continuous and uninterruptedby axial grooves or beams and having a pitch diameter which tapers fromadjacent one end toward the opposite end, throughout the entire lengthof said bore, at an included angle within the range of from about 1° to2°, having a substantially fully formed thread profile adjacent said oneend, and having a crest which is truncated to an increasing degree fromadjacent said substantially fully formed thread profile to adjacent saidopposite end, said crest having a constant diameter from said one end tosaid opposite end, said threaded bore being dimensioned such that saidexteriorly threaded member can mate therewith and experience relativelyfree rotation relative to said body at said one end but will experienceinterference adjacent said opposite end, whereby said exteriorlythreaded member and said body can be threaded together and will becomelocked against loosening by vibration.
 4. The combination of claim 3,wherein said interference is such that it requires a torque within apredetermined range to unthread said exteriorly threaded member fromsaid nut.
 5. A locking nut comprising:a body having a threaded boreextending therethrough, the thread of said bore having a pitch diameterwhich tapers from one end of said body to its opposite end at anincluded angle of from about 1° to about 2°, said thread having a fullyformed root with a taper substantially the same as that of said pitchdiameter, said thread further having a crest which is of a constantdiameter, said crest being tuncated with the truncation increasing fromadjacent said cone end to adjacent said opposite end, whereby when abolt of constant diameter is threaded into said nut the thread of saidbolt will interfere with said thread of said nut to create a lockingeffect.
 6. The locking nut of claim 5, wherein the pitch diameter ofsaid thread is tapered throughout the entire length of said bore.
 7. Thelocking nut of claim 5, wherein said thread is continuous through saidbore and uninterrupted by axial grooves or beams.
 8. A locking nutcomprising:a substantially rigid, substantially unbendable body, saidbody having a threaded bore extending therethrough from one end of saidbody to an opposite end thereof, the thread of said bore having a pitchdiameter which tapers from said one end to said opposite end at anincluded angle of from substantially 1° to 2°, with said thread beingcontinuous and uniterrrupted by axial grooves or beams, and being ofsubstantially full dimension, except at the crest thereof, said crest ofsaid thread being increasingly truncated from said one end to saidopposite end, with said crest of said thread having a constant diameter,such that when an exteriorly threaded member of constant diameter isthreaded into said nut, the thread of said member will interfere withsaid thread of said nut to create interference and a locking effectresistant to vibration.
 9. The locking of claim 8, wherein the pitchdiameter of said thread is tapered throughout the entire length of saidbore.